A number of bioerodible or biodegradable polymers are known and are useful for controlled release of pharmaceuticals. Such polymers are described in, for example, U.S. Pat. No. 4,291,013, issued Sep. 22, 1981 to H. Wahlig, et al, U.S. Pat. No. 4,347,234, issued Aug. 31, 1982 to H. Wahlig, et al, U.S. Pat. No. 4,525,495, issued Jun. 25, 1985 to L.C. Dorman, et al, U.S. Pat. No. 4,570,629, issued Feb. 18, 1986 to A. Widra, U.S. Pat. No. 4,572,832, issued Feb. 25, 1986 to K. Kigasawa, et al, U.S. Pat. No. 4,587,268, issued May 6, 1986 to R.W. Pfirrmann, U.S. Pat. No. 4,638,045, issued Jan. 20, 1987 to J. Kohn, et al, U.S. Pat. No. 4,675,381, issued Jun. 23, 1987 to D. Bitchon, and U.S. Pat. No. 4,745,160, issued May 17, 1988 to J.R. Churchill, et al. Of particular interest is Kohn, et al U.S. Pat. No. 4,638,045 which utilizes non-peptide bonds between side chains on dipeptides with the side chains being bonded together by hydrolytically unstable bonds which are biodegradable. The products of hydrolysis of such compounds include the side chains of each monomer unit and are, therefore, not as fully biocompatible as might be desired.
The present invention is directed to overcoming one or more of the problems as set forth above.